Multi-layer polymeric fuel tanks are often used in the automotive industry because they are lighter in weight, have greater flexibility and are cheaper to manufacture than fuel tanks made of metal. Multi-layer polymeric fuel tanks typically include a tank wall composed of at least two layers of a high density polyethylene (HDPE) structural material and an ethylene vinyl alcohol copolymer (EVOH) hydrocarbon vapor barrier layer disposed between them. The fuel tanks may be manufactured by, for example, co-extruding the multiple layers into two sheets and vacuum forming each sheet to form two complementary sections or halves of the fuel tank, blow molding coextruded parisons into two shell sections of the fuel tank, blow-molding a coextruded cylindrical parison, or other fuel tank manufacturing processes known in the art. Component parts of a fuel system, such as a spout, a fuel pump, a vent valve, a weld cap and/or a fuel level sensor may be disposed in or on one or both sections of the tank, or may be disposed in or on one or more openings in the parison. The molded halves of the fuel tank or the openings in the parison may then be welded together and/or pinched closed. The welded junctures and the pinched regions form seams in the tank wall with a discontinuous EVOH barrier layer in those regions, thereby creating permeation windows through which fuel vapors pass more easily through the tank wall and to the atmosphere.